Intermediate Projects

 

The Gurney Slade

This is almost certainly the lowest cost way of getting on air with a phone signal! The RX is a Regenerative Tuned Radio Frequency (TRF) design so is able to copy the normal amateur modes of single sideband phone and Morse, as well as the Amplitude Modulated signals used by the broadcast stations on the Medium Waveband. You start by building the RX for the MW which should be easy to get going and so give an early confidence boost! For this you will need modern 32R phones, 9 battery or 12 volt supply, and a few metres of wire for an aerial! The RX uses just four transistors and has controls for the Tuning, Regen and RF gain. You can then easily adapt it for either the 80 or 160m amateur bands where, because it is a Regen TRF, you will be able to listen to the common amateur signals.

The transmitter uses Amplitude Modulation for the 80 or 160m band because this is the simplest, and hence cheapest, method of generating phone signals. The TX uses either a 3.69 MHz or a 2.0 MHz ceramic resonator to ensure you stay in the permitted band, but the frequency can be pulled down by the PCB mounted trimmer capacitor to the parts of the band normally used for AM by amateurs. For netting purposes, there is a switch to just turn on the transmitter's RF oscillator while the RX is active. When you wish to actually transmit, this is controlled by the PTT switch of your dynamic type of microphone. The maximum output power is about 0.75W on a 9 volt battery, or 1.5W on a 12 volt supply, so the AM carrier levels are normally set for 3/8 or 3/4 of a Watt. The TX uses five more of the same transistors as the RX, with two in parallel for the output stage, together with one integrated circuit. The TX output stage has a parallel tuned output circuit with three taps for the variety of aerials that might be encountered on these bands - especially if they are not full sized.

These features make the design ideal for radio Clubs where newcomers are to be introduced to home construction, and where Club nets can operate over a short ranges with simple aerials before advancing to more complex designs and longer distances. The kit price is GBP 38.

 

Halse and Hatch

The emphasis in this phone singe sideband design is ease of construction. The Halse RX can be used on its own but together they form a single band 5 Watt SSB TCVR for any single band of 20, 40 or 80m. The superhet's IF is 9 MHz which gives coverage of the 20 and 80m bands with a single VFO band near 5 MHz; and by just changing the VFO inductor it can work near 2 MHz for the alternative 40m band. Starting at the aerial, the receiver has a double tuned RF filter, followed by the first mixer which is an SA602 having its own discrete IF amp prior to the IF filter which uses four crystals in a ladder formation. The second mixer is also an SA602 which includes the Carrier Insertion Oscillator and can work on either sideband by the addition of an inductor. The first audio stage uses a pair of BS170 MOSFETs driving the AF gain control, which is followed by the audio output stage able to drive a loud speaker or phones. The RX PCB is nearest the front panel in the photo below. You can add the Mini CW kit, the Mini AGC, and or a digital frequency readout - the three digit one is most appropriate.

For transmission, the RX is switched over to produce low level SSB by installation of relays that come with the TX kit.  The microphone speech amplifier output is fed into the RX second mixer which now acts as a balanced modulator. The IF strip is then used in the reverse direction (with relays reversing the mixer inputs and outputs to reverse the signal flow), so that the IF filter removes the unwanted sideband and feeds into the other mixer to get to the desired band frequency. The RF BPF removes the unwanted mixer products so that low level SSB is actually ejected out of the RX aerial terminal! Then follows the TX RF amplifier chain with an IRF510 MOSFET for the RF output stage; this is designed to produce 5W on a nominal 12v supply, but as ever, it is highly dependent on actual supply volts at the output stage! This is followed by a double Pi harmonic filter with the inductors and capacitors adjusted for the chosen band. TR control is by your mic's PTT switch and this also mutes the RX when transmitting.

Prices are GBP 45 for the Halse RX, or GBP 78 for the Halse and the Hatch when ordered together. The Hatch is priced at GBP 35 when ordered on its own later.

 

Three 'Crystal' Isle

This is the simplest way to produce CW on more than one frequency! If all three frequencies are in the same band then no extra low pass harmonic filters are needed; but if they are for three bands then you also need a Dual LPF kit (plus the extra crystals) for the two extra filters not fitted on the Isle PCB. The selection of filters and crystals are done by DC signals from the rig's centre off toggle band switch. The other aspects of the transmitter are as in the single band Isle description. The Isle plus Dual LPF kit shown below (without extra crystals) costs GBP 29.

 

Three Band VFO schemes

When the Mini Mix kit is used with a Mk 2 Yeo to provide the Local Oscillator (LO) signal, it can easily provide outputs for 20, 40 and 80m simultaneously, so that three band reception and transmission with VFO control is possible. This avoids the problems of chirp or FMing when transmitting and also improves frequency stability, especially for the higher bands.  A simple centre off toggle switch can select the wanted LO output with another pole controlling the filter relays. For SSB, the Yeo's Fine control provides a plain band-spread action, whereas for CW, it provides RIT under control from the Isle.

If you have the Mini Mix kit with the Yeo, it can easily produce the LO signals for all three of 20, 40 and 80m, so it is only necessary to add the receiver's input RF input filters for all three band reception! The Yeo PCB is drilled for the extra parts as shown below. The Mini mixer kit has been fitted on the side here to keep the footprint small for ease of demonstration and compactness. These extra 3 band filter parts cost GBP 9.

Three Band VFO Controlled Isle & Yeo

The next step is to make the Yeo able to transmit CW on all three bands 20, 40 and 80m! Just feed the Mini Mix's LO signal also to the Isle which has to be fitted with the Dual LPF kit for the extra bands. This combination provides full VFO CW transceiver operation on 20, 40 and 80m as shown below! It comprises a Yeo with 3 band extras, Mini Mix kit, Isle and Dual LPF. The discounted price is GBP 75.

The Rimpton TX

This is intended primarily for Amplitude Modulated phone work on the lower frequency bands 40, 80 and 160m, and would be a good companion to the Rockwell receiver. For simplicity, frequency control is by crystal (or ceramic resonator/trimmer on the 80/160m bands) - the standard kit includes an 1843 KHz crystal to make it simpler for novice operators to match RX and TX frequencies. The peak output is 1.5W when using a nominal 12 volt supply which means that for AM, the nominal carrier output is 0.35W so allowing the 100 % modulation peak of 1.5W. This is enough for 'across playfield' type contacts on short aerials prior to attempting longer distances with larger aerials that are properly matched. The kit has a double Pi harmonic filter. The speech amplifier is intended for ordinary dynamic style microphones and is easily set up for AM using the on board RF rectifier in conjunction with your multi-meter. There are two switches, the left one activates only the RF oscillator to allow easy tuning of the RX to the transmit frequency, while the right hand one controls the transmitter (and receiver)  if the microphone does not have its own PTT switch. The kit includes an aerial changeover relay. The Rimpton price is 24 GBP.

 


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